A diecast mineralization process forms the tough mantis shrimp dactyl club.

Biomineralization, the process by which mineralized tissues grow and harden via biogenic mineral deposition, is a relatively lengthy process in many mineral-producing organisms, resulting in challenges to study the growth and biomineralization of complex hard mineralized tissues. Arthropods are ideal model organisms to study biomineralization because they regularly molt their exoskeletons and grow new ones in a relatively fast timescale, providing opportunities to track mineralization of entire tissues. Here, we monitored the biomineralization of the mantis shrimp dactyl club-a model bioapatite-based mineralized structure with exceptional mechanical properties-immediately after ecdysis until the formation of the fully functional club and unveil an unusual development mechanism. A flexible membrane initially folded within the club cavity expands to form the new club's envelope. Mineralization proceeds inwards by mineral deposition from this membrane, which contains proteins regulating mineralization. Building a transcriptome of the club tissue and probing it with proteomic data, we identified and sequenced Club Mineralization Protein 1 (CMP-1), an abundant mildly phosphorylated protein from the flexible membrane suggested to be involved in calcium phosphate mineralization of the club, as indicated by in vitro studies using recombinant CMP-1. This work provides a comprehensive picture of the development of a complex hard tissue, from the secretion of its organic macromolecular template to the formation of the fully functional club.

Calcium­dependent activation of PHEX, MEPE and DMP1 in osteocytes.

Calcium (Ca2+) signaling is the first messenger signal exhibited by osteocytes. The present study aimed to better understand the link between Ca2+ concentration, and the levels of bone mineralization regulator proteins [phosphate­regulating neutral endopeptidase on chromosome X (PHEX), matrix extracellular phosphoglycoprotein (MEPE) and dentin matrix protein 1 (DMP1)] and the levels of oxidative stress in osteocytes. The viability of MLO­Y4 cells was determined using the live/dead assay following treatment with various Ca2+ concentrations (1.8, 6, 12, 18, 24 and 50 mM) for different durations (15 and 60 min, and 24 h). Superoxide dismutase (SOD), catalase (CAT), glutathione (GSH) and NADPH oxidase (NOX) enzymes were analyzed using a colorimetric method. Apoptosis was detected by caspase­3 analysis. Furthermore, the protein expression levels of PHEX, MEPE and DMP1 were analyzed using immunoblotting, and oxidative stress was examined using the total antioxidant and total oxidant status (TOS) assay. Notably, after 15 min, there were more live cells than dead cells; however, after 60 min, the number of dead cells was increased following treatment with 24 and 50 mM Ca2+. After 24 h, there were more dead cells than live cells following treatment with 50 mM Ca2+. After 24 h of Ca2+ treatment, the highest protein expression levels of PHEX, MEPE and DMP1 were measured in cells treated with 24 mM Ca2+. In addition, as Ca2+ concentration increased, the TOS and the oxidative stress index values were also increased. In conclusion, these results suggested that 24 mM Ca2+ may trigger bone mineralization proteins, such as PHEX, MEPE and DMP1, and could be considered an applicable dosage for the treatment of bone damage in the future.